What does the Bible command about separation from the world?

The Bible tells us to be separate from the world, but this does not mean isolation from the world. The Lord Jesus, if you recall, spent time with sinners and was condemned for this by the self-righteous religious Pharisees. The point of separation is that we are not to live and think like the world nor be unequally yoked with them in such a way that it hinders or restricts us from being free to follow and obey the Lord. We are allowed to use and function in the world, otherwise we could not be much of a testimony.